This invention relates to a valve disabling device for internal combustion engines mainly adapted for use in motorcycles and other vehicles.
Conventional high output type internal combustion engines include a type which is equipped with a plurality of inlet valves and/or exhaust valves at each of the cylinders and thus adapted to permit large quantities of a mixture and/or exhaust gases to be supplied into and/or emitted from the engine cylinders. Also known in a valve disabling device for use with such high output type internal combustion engines, which is adapted to selectively hold the inlet valves and/or the exhaust valves in a first position wherein all the valves are rendered operative, and in a second position wherein part of the valves are rendered inoperative or disabled, to improve the output characteristic of the engine particularly in a low speed region.
A conventional valve disabling device of this kind includes first and second rocker arms provided for a pair of inlet valves and/or exhaust valves, one of which is engaged with a cam forming part of the valve actuating mechanism, a piston disposed within a cylinder bore formed in the first rocker arm, in a manner projectable toward and retractable away from the second rocker arm, and a guide pin disposed within a guide bore formed in the second rocker arm and permanently urged toward the first rocker arm. With this valve disabling device, when operating oil is supplied under high pressure to the cylinder bore from the hydraulic circuit connected thereto, the piston is forced into the guide bore by the operating oil against the urging force of the guide pin, thereby drivingly coupling the first and second rocker arms together. Then, as the cam engaging one of the two rocker arms rotates, the paired inlet valves and/or exhaust valves are actuated through the coupled rocker arms to make opening and closing actions in unison. On the other hand, when the high pressure operating oil is discharged from the cylinder bore, the piston is forced out of the guide bore by the urging force of the guide pin, to disconnect the two rocker arms from each other. Then, only one of the paired inlet valves and/or the exhaust valves, which corresponds to the rocker arm engaging the cam, is actuated to make opening and closing actions, while the other one of the valves is rendered inoperative or disabled. However, all the time during stoppage of the engine, an oil pump, which is driven by the engine to supply high pressure operating oil into the cylinder bore, is kept inoperative to hold the piston out of the guide bore by the urging force of the guide pin, thus holding the other one of the rocker arms not engaging the cam in a state disconnected from the same cam.
Further, in these engines equipped with a plurality of inlet valves and/or exhaust valves, each pair of the valves need to be opened and closed in synchronism with each other. To this end, in an engine equipped with the above-mentioned valve disabling device, it is necessary to subject the rocker arms which correspond to the paired valves to tappet adjustment, i.e. adjustment of the clearance between the cam and the rocker arms, with the rocker arms coupled together. However, the conventional valve disabling device is not provided with means for effecting such adjustment, making it difficult to perform with accuracy tappet adjustment of the rocker arm not engaging the cam during stoppage of the engine.